QUALITY ASSESSMENT OF MEDICAL DECISION-MAKING IN RADIATION ONCOLOGY -VARIABILITY IN TARGET VOLUME DELINEATION FOR BRAIN-TUMORS

The enormous developments in radiation technology open new horizons fo r improvements in local tumour control. However, the evolution from co nventional external beam radiotherapy planning to conformal therapy mi ght be hampered by the potential risk of over-reliance on the physicia n's capability of estimating the tumour extent from imaging modalities . The variability between 12 volunteering physicians in the delineatio n of tumour and target volume on the lateral orthogonal localisation r adiograph from CT was assessed for 5 brain tumours. The estimated tumo ur and target sizes varied, respectively with a factor of 1.3-2.6 and with a factor of 1.3-2.1. The anatomical location of the volumes showe d maximum variations from 11 to 27 mm in the cranio-caudal direction a nd from 14 to 21 mm in the fronto-occipital direction. For the 5 test cases, the tumour area on which all radiation oncologists agreed, repr esented only 25-73% of the corresponding mean tumour area. Although th e introduction of computed tomography in radiation treatment planning was proved to be a major step forwards for treatment planning in many tumour sites, the results of the present study on brain tumours demons trate that the subjective interpretation of the tumour extent based on CT images might be one of the largest factors contributing to the imp rovement of our present concept of radiation treatment planning. Howev er, more data are urgently needed to estimate the uncertainty in targe t volume delineation in different tumour sites and with different imag ing modalities such as MRI. One of the most exciting and contributing factors in accurate delineation of tumours for radiation treatment in the future might be in the field of computer-aided image correlation.